About Me

No, not THAT Bob Hoover :-) (ie, Robert A. "Bob" Hoover from Tennessee and perhaps the best pilot in the history of flight.)
The problem is that all Roberts get Bob-ed at birth and there isn't much we can do about it. When posting something about aviation I generally use 'R.S.Hoover' to prevent confusion.

Monday, November 20, 2006

VW - Kool Tin

Since my list query about sources for decent Kool tin (that is, not the Taiwanese tin foil grade, casual fit tin...) I’ve learned that Berg sells sturdy stuff and that the 1600cc non-North American vanagon engines also had such tin stock. I’ve read in one of your list posts that the Kool tin when used on a 1600 with properly modified upright tin can produce better cooling. Can you outline the tinware modifications necessary to make this work?

You mentioned leaving off the stock deflector plates and welding the Kool tin to stock tinware after modifications to get a tight fit. I could probably “wing” something based on this, but I’m hoping to benefit from your experience here and get some more detail so I don’t inadvertantly cutoff critical airflow with a less than astute mod ;).

Volkswagen leaves off the deflector plates when they install ‘kool tin’ lower shrouding. The deflector plates are not compatible with the tighter ‘kool-tin’ lower shrouding.

With the engine upside-down on the assembly-fixture and the push-rod tubes off, heads loose, trial fit the kool-tin, observing how it was meant to be fastened and exactly where it was meant to fit between the cylinder fins.

Stock VW kool-tin fits reasonably well but is rather loose, especially in the middle. Experience has shown the original method of installation was inadequate. The kool-tin always came loose, ended up down on top of the push-rod tubes.

The first and most obvious fix is to drill a couple of small holes through the central wedge . . . the part that goes between the cylinders . . . and thread some thin-gauge safety wire through the holes. With the engine right-side up you’ll see that it’s possible to cut & shape two short pieces of welding rod or heavy-gauge stainless steel safety wire to fit down into the cylinder fins and bridge the gap between the cylinders. This is what I use to secure the thin-gauge safety wire I’ve installed in the kool-tin, drawing the stuff up until it is tight to fins. I shape the tin-ware with rubber or plastic mallets where necessary, with my hands in other areas, grinding or cutting away anything that prevents a smooth, symmetrical fit

To insure the sides can not come free I use two procedures. At the rear of the engine I modify the air-dams that fasten to the cylinder tin (and trap the breast tin between them) to form a smooth fit with the kool-tin, typically by snipping the metal into a series of fingers, heating them and molding each finger to the shape of the kool tin, all this while the tin-ware is securely fastened in position. Each little finger is tack-welded using a aircraft torch with a small tip. When the thing is well secured I take it off, weld it up, sand-blast it and otherwise prepare it for painting.

At the front of the engine, in order for the kool-tin to fit, you must modify the basic bottom-tin-ware pieces, a full-length piece on the driver’s side of the engine, a shorter piece on the side of the engine mounting the thermostat bracket. The modification is simply doing whatever is needed to make the tin-ware fit with the kool-tin in place. Typically, this means reducing the convoluted curves and indentations of the original piece, which formed a very critical part of the engine’s shrouding, into a simply curved panel that will accommodate the kool-tin. The convolutions, bulges and so forth are no longer required since their function is being performed by the Kool-tin.

To insure a good mechanical fit, I then fabricate a flange of sheet-metal of a suitable thickness to fit between the upper and lower pieces of tin-ware (i.e., the cylinder head tin-ware and the lower tin-ware) of sufficient depth and shape (I put a little lip on it) to allow it be welded to the kool-tin. The lower-tin-ware is removed while this fitting and welding is going on, of course. It’s usually necessary to fasten the kool-tin into the proper position with wire or by some other means in order to accomplish the weld . . .once you remove the lower tin-ware, the kool-tin is no longer held in position and will move around on you. I generally tack the flange at a couple of points then reassemble the lower tin-ware to be sure I’ve gotten it right. You’re after a really snug fit here, something that will force air to flow through the fins rather than around them.

Once I have a nice fit fore & act I clean the welds and paint the parts. This work should be done well ahead of any actual engine assembly.

The work doesn’t have to be pretty . . . no one is ever going to see it . . . but do the best you can, taking a bit of time to forge and grind your welds. You’ll have to use gas-welding, the tin-ware is a bit thin for MIG. And the thin stuff is prone to cracking so it pays to make a good job of it. Some of my first efforts were merely tacked together. They held up remarkably well but were not nearly so tight as fully-welded units.

On average, I spend about forty hours making up the tin-ware for a big-bore stroker. On the wider engines you must even modify the thermostat bracket... and make a new thermostat rod.

Except for final fitting, all of this work should be done on a mock-up since the welding, grinding and so forth might cause damage to a real engine. (A mock-up is any suitable crankcase . . . even one with a hole in it . . . fitted with suitable jugs & spacers to give the proper width.)

Welding the flange & air-dam to the kool-tin improves its stiffness but you’ll find the center is still ‘soft’. Although I continue to use the safety-wire fasteners, I also weld a couple of pieces of heavy wire across the bottom, exterior of the kool-tin. Normally, doing this would prevent the stock kool-tin from being removed but after the kool-tin has been modified there is no need to retain the stock securing notches other than as locators. With the notches ground into smooth ‘U’s the kool-tin drops into place on the head-studs without the bending required of the stock kool-tin. The welded wire stiffeners are about 1/8" in diameter and the width of the flat portion of the kool-tin. They add a remarkable amount of stiffness to the kool-tin, allowing it to be fastened more securely, eliminating any vibration that may develop.

I think it would be very difficult to not get better cooling using tighter lower shrouding, unless you installed it in such a manner that it could come loose. Some of the most valuable time you can spend would be to study the lower shrouding on the Corvair, VW Type IV, and most aircraft engines enclosed in pressure-cowlings. When you compare these more efficient cowling methods to the early VW engine it will make the short-comings of the deflector plates painfully evident.

Proper shrouding improves the efficiency of your cooling system. Not only will it cause your engine to run cooler, tighter shrouding allows the thermostat to keep the engine at a more even temperature, which greatly improves the engines service life.

1 comment:

Anonymous
said...

true the tin cools. My 1st bug, a 66 had some tin/didn't have some. Not knowing much about the motors at the time, I just drove it - for 3 months until I burned a "moon shape" in a piston, and smoked out the driver behind me. He lived and I learned. My current 62' is much "cooler" - good read -